Motor vehicle tires can no longer be considered as merely constituting an accessory item of equipment on a motor vehicle, but are effectively an important structural element thereof. It is precisely from the point of view of safety and driving and road-holding characteristics at elevated speeds that a satisfactory set of tires on a motor vehicle is absolutely necessary. However, in the production of motor vehicle tires, it is invevitable that the production process will involve deviations from the desired tire shape and configuration, and they can have considerable effects on the vehicle from the point of view of safety.
If an effort to remedy that situation, besides the conventional tire testing procedures such as ascertaining unbalance of the tire measuring radial and lateral out-of-truth or run-out of the tires, procedures for testing tires in respect of uniformity when subjected to forces acting thereon, and for testing tires in respect of bead characteristic parameters are operations which are becoming more and more important in modern times. In particular the bead contact pressure with which the tire is fitted on to a wheel rim is a factor of major significance. Especially when a vehicle is travelling at high speeds and when it is negotiating a curve, a tire is subjected to high forces which tend to pull it off the motor vehicle wheel rim. If those forces overcome the resilient forces opposed thereto on the part of the tire and by the inflation pressure therein, the wheel may suffer from the feared rim-off effect, namely a situation in which the tire jumps off the rim. On the other hand, the tire seating forces with which the tire is carried on the rim should not exceed certain levels as otherwise it becomes very difficult if not impossible to fit the tire to a wheel.
One form of apparatus for testing motor vehicle tires in particular with a view to preventing the occurence of the abovementioned rim-off effect, is to be found in German patent specification No. 1 773 367. That apparatus comprises clamping means which are applied against the inner bead of the tire, distributed around the circumference of a circle, and are displaceable in an outward direction. The apparatus has force measuring means which are associated with respective ones of the clamping means, for measuring and recording, in relation to peripheral angle of the tire, the compression forces with which the clamping means, which can be in the form of clamping jaws, are pushed over the same distances against the inner bead of the tire. In that way it is possible to arrive at an accurate picture about the bead parameters of the tire.